Plasma display apparatus and method of driving the same

This application claims the benefit of Korean Patent Application No. 10-2006-0127015 filed on Dec. 13, 2007, which is hereby incorporated by reference.

1. Field of the Disclosure

This document relates to a plasma display apparatus and a method of driving the same.

2. Description of the Related Art

A plasma display apparatus comprises a plasma display panel (PDP) for displaying an image and drivers for supplying driving voltages to the PDP.

The PDP comprises discharge cells partitioned off by barrier ribs. The discharge cells are filled with a main discharge gas such as neon (Ne), helium (He), or a gas mixture of Ne and He (Ne+He) and an inert gas comprising a small amount of xenon.

When a radio frequency voltage is applied to the discharge cells, vacuum ultraviolet (UV) rays are generated by discharge and the vacuum UV rays emit light from a phosphor applied between the barrier ribs.

The PDP comprises a plurality of electrodes and the drivers are connected to the PDP to supply the driving voltages to the electrodes. The drivers supply driving signals for displaying an image on the PDP to the electrodes when the PDP is driven.

On the other hand, since the discharge characteristic and the driving characteristic of the plasma display apparatus can vary in accordance with the driving signals supplied by the drivers, researches for optimizing the driving characteristic of the plasma display apparatus are continuously performed.

A plasma display apparatus according to the present invention comprises a plasma display panel comprising a first electrode and a second electrode and a driver alternately supplying a first sustain signal and a second sustain signal to the first electrode and the second electrode in a first subfield and supplying a third sustain signal and a fourth sustain signal that swing a positive polar voltage and a negative polar voltage in a second subfield to the first electrode and the second electrode.

A method of driving a plasma display apparatus according to the present invention comprises alternately supplying a first sustain signal and a second sustain signal to the first electrode and the second electrode in a first subfield and supplying a third sustain signal and a fourth sustain signal that swing a positive polar voltage and a negative polar voltage to the first electrode and the second electrode in a second subfield.

The implementation of this document will be described in detail with reference to the following drawings in which like numerals refer to like elements.

FIG. 1 illustrates a plasma display apparatus according to an embodiment of the present invention;

FIG. 2 illustrates the plasma display panel (PDP) of FIG. 1 ;

FIG. 3 illustrates the driving signals of the plasma display apparatus of FIG. 1 ;

FIG. 4A illustrates the scan driver or the sustain driver of FIG. 1 ;

FIG. 4B illustrates the operation of the scan driver or the sustain driver of FIG. 4A ; and

FIG. 5 describes a driver for driving sustain electrodes in a plasma display apparatus according to the present invention.

Embodiments will be described in a more detailed manner with reference to the drawings.

As illustrated in FIG. 1 , a plasma display apparatus according to an embodiment of the present invention comprises a plasma display panel (PDP) 100 , a driver 105 , a controller 140 , and a driving voltage generator 150 . The driver 105 comprises a scan driver 110 , a data driver 120 , and a sustain driver 130 .

As illustrated in FIG. 2 , the PDP 100 comprises a top surface panel 210 and a bottom surface panel 220 . A scan electrode 212 and a sustain electrode 213 run parallel with each other on the top surface substrate 211 of the top surface panel. The scan electrode 212 and the sustain electrode 213 can comprise transparent electrodes 212 a and 213 a formed of transparent indium tin oxide (ITO) and bus electrodes 212 b and 213 b formed of a metal. In addition, the scan electrode 212 and the sustain electrode 213 can comprise only the bus electrodes 212 b and 213 b . An upper dielectric layer 214 covers the scan electrode 212 and the sustain electrode 213 to insulate the scan electrode 212 and the sustain electrode 213 from each other. A protective layer 215 is provided on the upper dielectric layer 214 and emits secondary electrons to facilitate discharge.

Data electrodes 223 are arranged on the bottom surface substrate 221 of the bottom surface panel 220 to intersect the scan electrode 212 and the sustain electrode 213 . A lower dielectric layer 225 covers the data electrodes 223 to insulate the data electrodes 223 from each other. Barrier ribs 222 for partitioning off discharge cells are positioned on the lower dielectric layer 225 . R, G, and B phosphors 224 are applied between the barrier ribs 222 .

As illustrated in FIG. 3 , the scan driver 110 of the driver 105 supplies reset signals for initializing the wall charges of all of the discharge cells in a reset period to the scan electrodes under the control of the controller 140 . The set up signal Set-up of the reset signals forms excessive wall charges in the discharge cells and supplies the set down signal Set-down of the reset signals to the scan electrodes Y 1 to Yn.

The scan driver 110 sequentially supplies scan signals Scan that fall from a scan reference voltage Vsc to a scan voltage −Vy in an address period to the scan electrodes under the control of the controller 140 . The data driver 120 supplies data signals Data to data electrodes in synchronization with the scan signals Scan. Therefore, discharge cells to emit light in a sustain period are selected.

The sustain driver 130 supplies a bias voltage Vz to sustain electrodes in the reset period and the address period to facilitate address discharge between the scan electrodes and the data electrodes. The bias voltage Vz can be actually equal to a sustain voltage Vs.

The driver 105 alternately supplies a first sustain signal sus 1 and a second sustain signal sus 2 to the scan electrodes and the sustain electrodes under the control of the controller 140 in the sustain period of a first sub field. That is, the scan driver 110 of the driver 105 supplies the first sustain signal sus 1 to the scan electrodes and the sustain driver 130 of the driver 105 supplies the second sustain signal sus 2 to the sustain electrodes. The highest voltage of the first sustain signal sus 1 and the second sustain signal sus 2 is the sustain voltage Vs.

In addition, the driver 105 supplies a third sustain signal sus 3 and a fourth sustain signal sus 4 that swing a positive polar voltage and a negative polar voltage in the sustain period of a second subfield to the scan electrodes and the sustain electrodes under the control of the controller 140 . That is, the scan driver 110 of the driver 105 supplies the third sustain signal sus 3 to the scan electrodes and the sustain driver 130 of the driver 105 supplies the fourth sustain signal sus 4 to the sustain electrodes.

The first subfield and the second subfield can be continuously arranged and may not be continuously arranged. In addition, the first subfield and the second subfield can be comprised in one frame and can be comprised in different frames.

The highest voltage and the lowest voltage of the third sustain signals sus 3 and the fourth sustain signal sus 4 can be Vs/2 and −Vs/2. In addition, when the highest voltage of the third sustain signal sus 3 is supplied, the lowest voltage of the fourth sustain signal sus 4 can be supplied and, when the lowest voltage of the third sustain signal sus 3 is supplied, the highest voltage of the fourth sustain signal sus 4 can be supplied.

While the highest voltage of the first sustain signal sus 1 or the second sustain signal sus 2 is supplied, a voltage difference between the scan electrodes and the sustain electrodes can be actually equal to a voltage difference between the scan electrodes and the sustain electrodes while the highest voltage of the third sustain signal sus 3 or the fourth sustain signal sus 4 is supplied or a voltage difference between the scan electrodes and the sustain electrodes while the lowest voltage of the third sustain signal sus 3 or the fourth sustain signal sus 4 is supplied.

For example, when the highest voltage and the lowest voltage of the first sustain signal sus 1 and the second sustain signal sus 2 are the sustain voltage Vs and a ground voltage CND and the highest voltage and the lowest voltage of the third sustain signal sus 3 and the fourth sustain signal sus 4 are Vs/2 and −Vs/2 while the highest voltage Vs of the first sustain signal sus 1 and the second sustain signal sus 2 or the highest voltage Vs/2 of the third sustain signal sus 3 and the fourth sustain signal sus 4 is supplied, a voltage difference between the scan electrodes and the sustain electrodes is the sustain voltage Vs.

A difference between the highest voltage of the first sustain signal sus 1 and the highest voltage of the third sustain signal sus 3 can be no less than ⅕ of the highest voltage of the first sustain signal sus 1 or the highest voltage of the third sustain signal sus 3 .

The controller 140 of FIG. 1 receives vertical and horizontal synchronizing signals and clock signals, generates timing control signals CTRX, CTRY, and CTRZ for controlling the operation timing and the synchronization of the drivers 120 , 130 , and 140 in the reset period, the address period, and the sustain period, and supplies the timing control signals CTRX, CTRY, and CTRZ to the corresponding drivers 120 , 130 , and 140 to control the drivers.

The data control signal CTRX comprises a sampling clock for sampling data, a latch control signal, a switch control signal for controlling the on and off times of a sustain driving circuit and a driving switch element. The scan control signal CTRY comprises a switch control signal for controlling the on and off times of a sustain driving circuit and a driving switch element in the scan driver 110 . The sustain control signal CTRZ comprises a switch control signal for controlling the on and off times of a sustain driving circuit and a driving switch element in the sustain driver 130 .

The driving voltage generator 150 generates a set up voltage Vsetup, the scan reference voltage Vsc, the scan voltage −Vy, the sustain voltage Vs, and a data voltage Va. The driving voltages can change in accordance with the composition of discharge gases or a discharge cell structure.

The driver 105 according to the present invention supplies different sustain signals in the first subfield and the second subfield in order to improve the driving characteristic of the PDP to correspond to the various driving conditions of the plasma display apparatus. For example, the driving conditions of the plasma display apparatus can comprise gray scale weight values of the first subfield and the second subfield, the temperature of the PDP, the average picture level (APL) of an image signal, the number of frames displayed on the PDP per a second, and the kind of a displayed image.

For example, when the gray scale weight value of the first subfield is smaller than the gray scale weight value of the second subfield, that is, when the number of light-emission times in one discharge cell where addressing discharge is generated in the sustain period of the first subfield due to sustain discharge is smaller than the number of light-emission times in one discharge cell where the addressing discharge is generated in the sustain period of the second subfield, the driver 105 supplies the first sustain signal and the second sustain signal to the scan electrodes and the sustain electrodes in the first subfield and supplies the third sustain signal and the fourth sustain signal to the scan electrodes and the sustain electrodes in the second subfield.

When the gray scale weight values increase, the number of sustain signals increases in the sustain period. Therefore, high voltage sustain signals are supplied, electromagnetic interference (EMI) is remarkably generated, opposed discharge increases between the scan electrodes and the data electrodes or the sustain electrodes and the data electrodes, and phosphors are damaged due to the opposed discharge so that latent image is generated. Therefore, according to an embodiment of the present invention, since low voltage sustain signals are supplied in a subfield where the gray scale weight values are large, the EMI, the opposed discharge, and the damage of the phosphors are remarkably reduced so that the latent image is reduced.

The temperature sensor 160 of FIG. 1 measures the temperatures of the PDP in the first subfield and the second subfield to output a temperature information signal to the controller 140 . The controller 140 compares the temperatures of the PDP in the first subfield and the second subfield with a reference temperature. At this time, the first subfield and the second subfield are comprised in different frames.

When the temperature of the PDP in the first subfield is higher than the reference temperature and the temperature of the PDP in the second subfield is lower than the reference temperature, the scan driver 110 and the sustain driver 130 of the driver 105 reduces the number of sustain signals supplied in the first subfield and increases the number of sustain signals supplied in the second subfield in accordance with the control of the controller 140 .

That is, when the temperature of the PDP is higher than the temperature of the PDP in the second subfield in the first sustain period, the driver 105 can supply the first and second sustain signals sus 1 and sus 2 in the first subfield period and can supply the third and fourth sustain signals sus 3 and sus 4 in the second subfield.

When the number of sustain signals increases in the second subfield where the temperature of the PDP is low, when the high voltage first and second sustain signals sus 1 and sus 2 are supplied, the EMI, the opposed discharge, the damage of the phosphors, and the latent image are reduced.

Therefore, according to an embodiment of the present invention, in the second subfield where the temperature of the PDP is low, the driver 105 supplies the third and fourth sustain signals sus 3 and sus 4 that swing the highest voltage and that lowest voltage of small magnitude to the scan electrodes and the sustain electrodes. Therefore, the EMI, the opposed discharge, and the damage of the phosphors are remarkably reduced so that the latent image is reduced.

The APL calculator 170 of FIG. 1 outputs the APLs of a first frame and a second frame to the controller 140 . The controller 140 reduces the number of sustain signals when the APL increases and increases the number of sustain signals when the APL is reduced. When the APL of the first frame is higher than the APL of the second frame, the driver 105 can supply the first sustain signal and the second sustain signal in the first subfield comprised in the first frame and can supply the third sustain signal and the fourth sustain signal in the second subfield comprised in the second frame. Therefore, the low voltage sustain signals are supplied in the second frame where the APL is small and the number of sustain signals increases so that the EMI, the opposed discharge, the damage of the phosphors, and the latent image are reduced.

In addition, when m frames are displayed on the PDP per a second, the driver 105 can supply the first sustain signal and the second sustain signal and, when n (n>m) frames are displayed on the PDP per a second, the driver 105 can supply the third sustain signal and the fourth sustain signal. For example, when the PUP is driven by 50 Hz, the driver 105 supplies the high voltage first sustain signal and second sustain signals and, when the PDP is driven by 60 Hz, the driver 105 can supply the low voltage third sustain signal and fourth sustain signal. When the high voltage sustain signals are supplied while the number of frames displayed per a second increases, since the EMI, the opposed discharges the damage of the phosphors, and the latent image increase, according to an embodiment of the present invention, the low voltage third sustain signal and fourth sustain signal are supplied.

The controller 140 determines whether an image signal input from the outside is a moving image or a still image to control the driver 105 . The controller 140 can determine that the input signal is the moving image when a change in gray scale values is larger than a reference value. The driver 105 can supply the first sustain signal and the second sustain signal when the moving image is displayed on the PDP and can supply the second sustain signal when the still image is displayed on the PDP. When the high voltage first sustain signal and second sustain signal are supplied while the still image is displayed, since the phosphors of a specific discharge cell are damaged for a long time, the latent image can be remarkably generated. Therefore, when the low voltage third sustain signal and fourth sustain signal are supplied while the still image is displayed according to an embodiment of the present invention, the damage of the phosphors and the latent image are reduced.

As illustrated in FIG. 4A , the scan driver or the sustain driver of FIG. 1 comprises a first voltage supplier 410 , a second voltage supplier 420 , a signal forming unit 430 , and an energy storage unit 440 .

The first voltage supplier 410 comprises a first switch Q 1 for supplying the highest voltage of the first and second sustain signals, a second switch Q 2 and a third switch Q 3 for supplying the highest voltage of the third and fourth sustain signals, and a fourth switch Q 4 turned on when the highest voltage of the first to fourth sustain signals is supplied.

The second voltage supplier 420 comprises a fifth switch Q 5 for supplying the highest voltage of the first sustain signal and the second sustain signal, a sixth switch Q 6 for supplying the lowest voltage of the third sustain signal and the fourth sustain signal, and a seventh switch Q 7 turned on when the lowest voltage of the first to fourth sustain signals is supplied.

The signal forming unit 430 supplies or recovers energy through resonance to form the first to fourth sustain signals.

The energy storage unit 440 comprises a capacitor Cs for storing energy and the seventh switch Q 7 and an eighth switch Q 8 for supplying the reference voltage of the capacitor Cs.

As illustrated in FIG. 4B , the eighth switch Q 8 of the energy storage unit 440 and the 10 th switch Q 10 of the signal forming unit 430 are turned on and the remaining switches are turned off. Therefore, resonance is formed between an inductor L and the PDP so that the voltage of the scan electrodes Y or the sustain electrodes Z gradually increases from the ground voltage to the sustain voltage Vs.

The first switch Q 1 , the second switch Q 2 , the fourth switch Q 4 , and the eighth switch Q 8 are turned on and the remaining switches are turned off. Therefore, the voltage of the scan electrodes Y or the sustain electrodes Z is sustained as the sustain voltage Vs and the capacitor C of the first voltage supplier 410 is filled with the sustain voltage Vs. In particular, the seventh Q 7 is turned off and the body diode of the seventh switch Q 7 intercepts the sustain voltage Vs supplied to the scan electrodes Y or the sustain electrodes Z.

The eighth switch Q 8 and the 11 th switch Q 11 are turned on and the remaining switches are turned off. Therefore, resonance is formed between the inductor L and the PDP so that the voltage of the scan electrodes Y or the sustain electrodes Z is gradually reduced from the sustain voltage Vs to the ground voltage.

The fifth switch Q 5 , the seventh switch Q 7 , and the eighth switch Q 8 are turned on and the remaining switches are turned off. Therefore, the voltage of the scan electrodes Y or the sustain electrodes Z is sustained as the ground voltage GND. The first sustain signal sus 1 or the second sustain signal sus 2 is formed through the above-described processes.

As illustrated in FIG. 4B , the ninth switch Q 9 of the energy storage unit 440 and the 10 th switch Q 10 of the signal forming unit 430 are turned on and the remaining switches are turned off. Therefore, resonance is formed between the inductor L and the PDP so that the voltage of the scan electrodes Y or the sustain electrodes Z gradually increases from −Vs/2 to Vs/2.

The third switch Q 3 , the fourth switch Q 4 , and the ninth switch Q 9 are turned on and the remaining switches are turned off. Therefore, since −Vs/2 is supplied to the capacitor C of the first voltage supplier 410 and the sustain voltage Vs is filled in the capacitor C, the voltage of the scan electrodes Y or the sustain electrodes Z is sustained as Vs/2. In particular, the seventh switch Q 7 is turned off and the body diode of the seventh switch Q 7 intercepts the Vs/2 supplied to the scan electrodes Y or the sustain electrodes Z.

The ninth switch Q 9 and the 11 th switch Q 11 are turned on and the remaining switches are turned off. Therefore, resonance is formed between the inductor L and the PDP so that the voltage of the scan electrodes Y or the sustain electrodes Z is gradually reduced from Vs/2 to −Vs/2.

The sixth switch Q 6 , the seventh switch Q 7 , and the ninth switch Q 9 are turned on and the remaining switches are turned off. Therefore, the voltage of the scan electrodes Y or the sustain electrodes Z is sustained as −Vs/2. The third sustain signal sus 3 or the fourth sustain signal sus 4 are formed through the above-described processes.

As illustrated in FIG. 5 , the fifth switch Q 5 and the seventh switch Q 7 can be common-source connected to each other.

The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing embodiments is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.